A solution resulting from allowing two molecules of trimethylaluminum (AlMe3) to react with one molecule of bis(cyclopentadienyl)titanium dichloride (Cp2TiCl2) with each other in a toluene solvent is called a Tebbe reagent, and it is known that a Tebbe complex (Cp2TiCH2AlClMe2, μ-chloro-μ-methylene-bis(η5-cyclopentadienyl)titanium dimethylaluminum) (hereinafter sometimes referred to simply as “Tebbe complex”) in this solution is useful as a catalyst component (see, for example, NPLs 1 to 5). In addition, it is also known that the Tebbe complex can be isolated from the Tebbe reagent by carrying out an operation of recrystallization (see PTL 1 and NPLs 1 to 2).
It is known that the Tebbe reagent or Tebbe complex is useful for hydrogenation of an unsaturated double bond of a conjugated diene portion of a conjugated diene polymer (see PTLs 1 to 5), a methylenation reaction of a carbonyl compound, and so on.
It is reported that the high-purity Tebbe complex can be acquired in a purity of 80 to 90% and a yield of 49% by allowing 62 g (0.25 mol) of bis(cyclopentadienyl)titanium dichloride and 48 mL (0.25 mol) of trimethylaluminum to react with each other in 250 mL of toluene at room temperature for 60 hours. Although it is reported that a red-orange crystalline Tebbe complex whose elemental analysis is coincident can be acquired by recrystallizing this crude product from a toluene solution of trimethylaluminum and subsequently pentane, the yield of the foregoing Tebbe complex is not certain (see NPL 1).
Similarly, it is disclosed that bis(cyclopentadienyl)titanium dichloride (0.1 mol) and trimethylaluminum (0.2 mol) are allowed to react with each other in a toluene solvent at room temperature for 60 hours, and a residue from which a volatile component has been distilled off is recrystallized from toluene, whereby 14 g (0.049 mol) of a Tebbe complex can be acquired. Furthermore, it is disclosed that by recrystallizing this from trimethylaluminum-containing toluene and pentane, 9.5 g (0.033 mol) of a red-orange crystalline Tebbe complex having a purity to such an extent that impurities are not observed by 1H-NMR analysis can be acquired (see PTL 1).
It is known that a formation rate of the Tebbe complex in the Tebbe reagent varies with an amount of trimethylaluminum relative to titanocene dichloride, a temperature, a time, and a dielectric constant of the solvent (see NPL 3). Furthermore, it is known that a purity of the Tebbe complex is lowered according to the kind of the solvent for depositing a crystal of the Tebbe complex from the Tebbe reagent (see NPL 2).
It is reported that in view of the fact that not only the Tebbe complex contained in the Tebbe reagent is sensitive to air or humidity, but also even if the Tebbe complex is stored in an inert gas atmosphere, it is decomposed, it is preferred to use the Tebbe complex rapidly after preparation (see NPLs 4 to 5). In addition, it is reported that even a single crystal of the Tebbe complex is liable to be decomposed (see NPL 2).
As a method for enhancing the storage stability of the Tebbe complex, there is disclosed a method in which at least one of an oxygen-containing organic compound having 2 or more carbon atoms and a nitrogen-containing compound or a compound composed of a salt thereof is made coexistent relative to a Tebbe complex-containing solution; and it is disclosed that even when the aforementioned Tebbe complex-containing solution having been subjected to chilled storage for 2 months is used for a hydrogenation catalyst of a styrene/butadiene-based block polymer, the catalytic activity does not substantially change (see PTL 1).